The present invention relates to a capacitor and a capacitively-coupled isolator circuit for providing ground reference potential isolation in an integrated circuit package.
Isolator circuits are used to couple signals between circuits having different ground reference potentials. In some situations, the respective grounds can have a difference in potential as high as several thousand volts. Generally, there are three methods for providing isolation between circuits having different ground reference potentials: opto-coupled isolation, transformer-coupled isolation, and capacitively-coupled isolation. Opto-coupled and transformer-coupled isolation techniques suffer the disadvantage that the coupling devices are relatively bulky and not well suited for use in an integrated circuit. Capacitors, on the other hand, can be made smaller and can be integrated on a semiconductor die.
However, attempts in the past to provide a capacitively-coupled isolator circuit on a single semiconductor die have been met with problems due to reliability constraints and damage from electrostatic discharging and overvoltage breakdown. In particular, it has been found to be difficult to provide silicon dioxide-based capacitors capable of withstanding the high voltage differentials commonly encountered in isolator circuits.
An alternative solution described in the prior art is to form isolation capacitors on a ceramic substrate disposed in a plastic encapsulated integrated circuit package between two semiconductor dies containing the input and output stages of the isolator circuit (see, e.g., Meinel U.S. Pat. No. 4,780,795). However, such a hybrid structure requires that the isolation capacitors be premanufactured on a separate substrate apart from the plastic package.
In view of the foregoing, it would be desirable to provide a capacitor that can withstand high voltage differentials and that can be implemented as an isolation capacitor in an integrated circuit package without an additional substrate.
It would also be desirable to provide an isolator circuit that can be fabricated in a single integrated package.